Lubricant knowledge

Lubricant knowledge

Lubricating oil knowledge

1. Lubricating oil function Lubricating oil is a liquid lubricant used on various types of machinery to reduce friction and protect machinery and processed parts. It mainly plays the role of lubrication, cooling, rust prevention, cleaning, sealing and buffering. Lubricating oil accounts for 85% of all lubricating materials, and there are many types and brands. Now the world's annual consumption is about 38 million tons. The general requirements for lubricants are: (1) Anti-friction and anti-wear, reduce frictional resistance to save energy, reduce wear to extend mechanical life, and improve economic efficiency; (2) Cooling requires that frictional heat be discharged from the machine at any time; (3) (4) Anti-corrosion and anti-rust, requiring protection of the friction surface from oil deterioration or external corrosion; (5) Cleaning and washing, requiring the friction area to be cleaned and removed; (6) ) Stress dispersion buffering, dispersing load and mitigating impact and shock absorption; (7) Kinetic energy transmission, hydraulic system, remote control motor and friction stepless speed change.

2. Lubricating oil composition Lubricating oil generally consists of two parts: base oil and additives. Base oil is the main component of lubricating oil and determines the basic properties of lubricating oil. Additives can make up for and improve the performance of base oils and give some new properties. It is an important part of lubricating oil. 1. Lubricating oil base oil Lubricating oil base oil is mainly divided into two categories: mineral base oil and synthetic base oil. Mineral base oils are widely used and used in large amounts (about 95% or more). However, in some applications, products formulated with synthetic base oils must be used, which has led to rapid development of synthetic base oils. Mineral oil base oil is refined from crude oil. The main production processes of lubricating base oil include: atmospheric and vacuum distillation, solvent deasphalting, solvent refining, solvent dewaxing, clay or hydrogenation supplement refining. In 1995, my country's current lubricant base oil standards were revised, mainly the classification method was revised, and two types of special base oil standards, low condensation and deep refined, were added. In the production of mineral lubricants, the most important thing is to select the best crude oil. The chemical composition of mineral base oils includes high boiling point, high molecular weight hydrocarbons and non-hydrocarbon mixtures. Its composition is generally alkane (straight chain, branched chain, multi-branched chain), cycloalkane (monocyclic, bicyclic, polycyclic), aromatic hydrocarbon (monocyclic aromatic hydrocarbon, polycyclic aromatic hydrocarbon), cycloalkyl aromatic hydrocarbon and oxygen-containing, nitrogen-containing , Sulfur-containing organic compounds and non-hydrocarbon compounds such as gums and asphaltenes.

2. Additives Additives are the essence of modern high-grade lubricants. Correct selection and reasonable addition can improve their physical and chemical properties, impart new special properties to the lubricant, or enhance some of its original properties to meet higher requirements. According to the required quality and performance of lubricants, careful selection of additives, careful balance, and reasonable deployment are the key to ensuring the quality of lubricants. Commonly used additives are: viscosity index improvers, pour point depressants, antioxidants, detergents, dispersants, friction reducers, oily agents, extreme pressure agents, antifoaming agents, metal deactivators, emulsifiers, corrosion inhibitors, Rust agent, demulsifier. Third, the basic performance of lubricating grease Lubricating oil is a technology-intensive product, a complex mixture of hydrocarbons, and its real performance is the comprehensive effect of complex physical or chemical changes. The basic properties of lubricants include general physical and chemical properties, special physical and chemical properties and simulated bench tests. General physical and chemical properties Each type of lubricating grease has its common physical and chemical properties to show the inherent quality of the product. For lubricants, these general physical and chemical properties are as follows: (1) Appearance (chromaticity) The color of the oil can often reflect its degree of refinement and stability. For base oils, generally, the higher the degree of refining, the cleaner the hydrocarbon oxides and sulfides are removed, and the lighter the color. However, even if the refining conditions are the same, the color and transparency of base oils produced from crude oils of different oil sources and bases may be different. For new finished lubricants, due to the use of additives, color has lost its original meaning as an index for judging the degree of refinement of the base oil. (2) Density Density is the simplest and most commonly used physical performance index for lubricants. The density of lubricating oil increases with the increase in the amount of carbon, oxygen, and sulfur in its composition. Therefore, at the same viscosity or the same relative molecular mass, the lubricating oil contains more aromatic hydrocarbons, and contains more gums and asphaltenes. The density is the highest, the one with more cycloalkanes is in the middle, and the one with more alkanes is the smallest. (3) Viscosity Viscosity reflects the internal friction of oil, and is an indicator of oil properties and fluidity. Without adding any functional additives, the higher the viscosity, the higher the oil film strength and the worse the fluidity. (4) Viscosity index Viscosity index indicates the degree of oil viscosity change with temperature. The higher the viscosity index, the less the oil viscosity is affected by temperature, the better its viscosity-temperature performance, and vice versa. (5) Flash point Flash point is an indicator of oil vaporization. The lighter the distillate of the oil, the greater the evaporation and the lower its flash point. Conversely, the heavier the oil fraction, the less evaporative, and the higher its flash point. At the same time, the flash point is an indicator of the fire hazard of petroleum products. The hazard level of oil products is divided according to the flash point. The flash point is flammable below 45℃, and flammable above 45℃. It is strictly forbidden to heat the oil to its flash point temperature during the storage and transportation of the oil. . In the case of the same viscosity, the higher the flash point, the better. Therefore, the user should choose according to the operating temperature and working conditions of the lubricant when choosing the lubricant. It is generally believed that the flash point is 20-30℃ higher than the operating temperature, and it can be used safely.(6) Freezing point and pour point Freezing point refers to the highest temperature at which the oil product stops flowing under specified cooling conditions. The solidification of oil is very different from the solidification of pure compounds. There is no clear solidification temperature for oil products.

The so-called "solidification" just loses fluidity as a whole, and not all components become solid. The freezing point of lubricating oil is an important quality index indicating the low-temperature fluidity of lubricating oil. It is of great significance for production, transportation and use. Lubricants with high freezing points cannot be used at low temperatures. On the contrary, in areas with higher temperatures, there is no need to use lubricating oils with low freezing points. Because the lower the freezing point of the lubricating oil, the higher the production cost, resulting in unnecessary waste. Generally speaking, the freezing point of lubricating oil should be 5~7℃ lower than the lowest temperature of the environment. But it should be mentioned in particular that when choosing low-temperature lubricating oil, the freezing point, low-temperature viscosity, and viscosity-temperature characteristics of the oil should be fully considered. Because of the low freezing point oil, its low temperature viscosity and viscosity-temperature characteristics may not meet the requirements. Both freezing point and pour point are indicators of low-temperature fluidity of oil products. There is no principled difference between the two, but the measurement method is slightly different. The freezing point and pour point of the same oil are not exactly the same. Generally, the pour point is higher than the freezing point by 2 to 3°C, but there are exceptions. (7) Acid value, base value and neutralization value Acid value is an index indicating that the lubricating oil contains acidic substances, and the unit is mgKOH/g.

There are two types of acid value: strong acid value and weak acid value. The combination of the two is the total acid value (TAN for short). What we usually call "acid number" actually means "total acid number (TAN)". Alkaline value is an index indicating the content of alkaline substances in lubricating oil, and the unit is mgKOH/g. The base number is also divided into two types: strong base number and weak base number. The combination of the two is the total base number (TBN for short). What we usually call "base number" actually refers to "total base number (TBN)". The neutralization value actually includes the total acid value and total base value. However, unless otherwise noted, the general term "neutralization value" actually only refers to the "total acid value", and its unit is also mgKOH/g. (8) Moisture Moisture refers to the percentage of water content in the lubricating oil, usually a weight percentage. The presence of moisture in the lubricating oil will destroy the oil film formed by the lubricating oil, make the lubricating effect worse, accelerate the corrosive effect of organic acids on metals, rust equipment, and make the oil easy to produce sediment. In short, the less water in the lubricant, the better. (9) Mechanical impurities Mechanical impurities refer to precipitates or colloidal suspensions in the lubricating oil that are insoluble in solvents such as gasoline, ethanol and benzene.

Most of these impurities are sand, gravel and iron filings, as well as some organic metal salts that are insoluble in solvents brought by additives. Generally, the mechanical impurities of the lubricating base oil are controlled below 0.005% (the mechanical impurities below 0.005% are considered as no). (10) Ash content and sulfuric acid ash Ash content refers to the non-combustible substances left after burning under specified conditions. The composition of ash is generally considered to be some metal elements and their salts. Ash content has different concepts for different oil products. For base oil or oil products without additives, ash content can be used to judge the refinement depth of oil products. For oils (new oils) added with metal salt additives, ash becomes a means to quantitatively control the amount of additives added. In foreign countries, sulfuric acid ash is used instead of ash. The method is to add a small amount of concentrated sulfuric acid before burning the oil sample after burning to convert the metal element of the additive into sulfate. (11) Carbon residue oil product under the specified experimental conditions, the coke-black residue formed after heated evaporation and combustion is called carbon residue. Residual carbon is an important quality indicator of lubricating oil base oil, and it is an item specified for judging the nature and refining depth of lubricating oil. The amount of carbon residue in the base oil of lubricating oil is not only related to its chemical composition, but also to the depth of oil refining. The main substances that form carbon residue in lubricating oil are: gums, asphaltenes and polycyclic aromatic hydrocarbons in the oil. . These substances are decomposed and condensed by strong heat under the condition of insufficient air to form carbon residue. The deeper the refining depth of the oil, the smaller its residual carbon value.

Generally speaking, the smaller the residual carbon value of the blank base oil, the better. At present, many oil products contain additives of metal, sulfur, phosphorus, and nitrogen, and their carbon residue value is very high. Therefore, the carbon residue of the additive oil has lost the original meaning of carbon residue determination. Mechanical impurities, moisture, ash and carbon residues are all quality indicators that reflect the purity of the oil and reflect the degree of refining the lubricating base oil. Special physical and chemical properties In addition to the above-mentioned general physical and chemical properties, each lubricant should also have special physical and chemical properties that characterize its use characteristics. The higher the quality requirement or the more specific oil, the more outstanding its special physical and chemical properties.

The test methods reflecting these special physical and chemical properties are briefly introduced as follows: (1) Oxidation stability Oxidation stability shows the anti-aging performance of lubricants. Some industrial lubricants with long service life have this index requirement, so they become these kinds of oils. A special performance required by the product. There are many methods to determine the oxidation stability of oil. Basically, a certain amount of oil is oxidized at a certain temperature for a certain time in the presence of air (or oxygen) and a metal catalyst, and then the acid value and viscosity of the oil are measured. Changes and formation of sediments. All lubricating oils have different auto-oxidation tendency depending on their chemical composition and external conditions. Oxidation occurs with the use process, which gradually generates some aldehydes, ketones, acids, gums, asphaltenes and other substances. Oxidation stability is the performance of inhibiting the formation of the above substances that are not conducive to the use of oil. (2) Thermal stability Thermal stability represents the high temperature resistance of oil, that is, the resistance of lubricating oil to thermal decomposition, that is, the thermal decomposition temperature. Some high-quality anti-wear hydraulic oils, compressor oils, etc. have put forward thermal stability requirements. The thermal stability of oil mainly depends on the composition of the base oil. Many additives with lower decomposition temperature often have an adverse effect on the stability of the oil; antioxidants cannot significantly improve the thermal stability of the oil. (3) Oiliness and extreme pressure oiliness is that the polar substances in the lubricating oil form a strong physical and chemical adsorption film on the metal surface of the friction part, thereby playing the role of high load resistance and friction and wear resistance, while extreme pressure is lubricating The polar substances of oil on the metal surface of the friction part undergo tribochemical decomposition under high temperature and high load, and then tribochemically react with the surface metal to form a soft (or plastic) extreme pressure film with a low melting point. It has the function of impact resistance, high load and high temperature lubrication. (4) Corrosion and rust are often caused by corrosion of steel and other non-ferrous metals due to oil oxidation or additives. The corrosion test is generally to put the copper strip in oil, place it at 100°C for 3 hours, and then observe the change of copper; while the rust test is to rust the steel surface under the action of water and water vapor. The determination of rust resistance is to Add 30ml of distilled water or artificial seawater to 300ml of test oil, then place the steel rod in it, stir for 24 hours at 54°C, and then observe whether the steel rod is corroded. The oil should have anti-metal corrosion and anti-corrosion effects. In the industrial lubricant standard, these two items are usually mandatory items. (5) Anti-foaming lubricating oil often produces foam due to the presence of air during operation, especially when the oil contains surface-active additives, it is easier to produce foam, and the foam is not easy to disappear. The foam produced during the use of lubricating oil will destroy the oil film, cause sintering of the friction surface or increase wear, and promote the oxidation and deterioration of the lubricating oil. It will also make the lubricating system air resistance and affect the lubricating oil circulation. Therefore, anti-foaming is an important quality index for lubricating oil.(6) Hydrolysis stability Hydrolysis stability characterizes the stability of oil products under the action of water and metals (mainly copper). When oil products have a high acid value or contain additives that are easily decomposed into acidic substances in contact with water, they often cause This indicator is unqualified. Its measuring method is to add the test oil to a certain amount of water, mix and agitate the copper slices at a certain temperature for a certain period of time, and then measure the acid value of the water layer and the weight loss of the copper slices. (7) Demulsibility industrial lubricants are often inevitably mixed with some cooling water during use. If the demulsibility of the lubricant is not good, it will form an emulsion with the mixed water, making it difficult for water to flow from the bottom of the circulating oil tank. Discharge, which may cause poor lubrication. Therefore, demulsibility is a very important physical and chemical property of industrial lubricants. For general oil products, 40ml test oil and 40ml distilled water are vigorously stirred at a certain temperature for a certain period of time, and then the time for the oil layer-water layer-emulsified layer to separate into 40-31-3ml; industrial gear oil is to mix the test oil with water, Stir at a certain temperature and 6000 rpm for 5 minutes, leave it for 5 hours, and then measure the number of milliliters of oil, water, and emulsified layer. (8) The air release value hydraulic oil standard has this requirement, because in the hydraulic system, if the air dissolved in the oil cannot be released in time, it will affect the accuracy and sensitivity of the hydraulic transmission, and it cannot be Meet the requirements of the hydraulic system. The method of measuring this performance is similar to that of anti-foaming, but it is to measure the release time of air (mist) dissolved in the oil. (9) Rubber sealability: Most people use rubber as seals in hydraulic systems. The oil in machinery inevitably comes in contact with some seals. Oils with poor rubber sealability can swell, shrink and harden rubber. , Cracks, affecting its sealing performance, so oil and rubber are required to have better adaptability. The hydraulic oil standard requires a rubber tightness index, which is measured by the change of a certain size of rubber ring after being immersed in oil for a certain period of time. (10) Shear stability When oils with tackifiers are added during use, due to the effect of mechanical shear, the high molecular polymers in the oils are sheared, reducing the viscosity of the oils and affecting normal lubrication. Therefore, shear stability is a special physical and chemical property that must be tested for this type of oil. There are many methods for measuring shear stability, including ultrasonic shearing method, nozzle shearing method, Wicks pump shearing method, and FZG gear shearing method. These methods are ultimately used to determine the viscosity drop rate of oil. (11) Solubility Solubility is usually expressed by aniline point. Different grades of oil have different solubility limits for compound additives. The limit value of low-ash oil is larger than that of over-alkaline oil, and the limit value of single-grade oil is larger than that of multi-grade oil. (12) The volatility of volatile base oil is related to fuel consumption, viscosity stability, and oxidation stability. These properties are especially important for multi-grade oils and energy-saving oils. (13) Anti-rust performance This refers specifically to the special physical and chemical properties of anti-rust grease. Its test methods include moisture test, salt spray test, laminated test, water replacement test, in addition to louver box test, long-term Storage test, etc. (14) Electrical performance Electrical performance is the unique performance of insulating oil, mainly including dielectric loss angle, dielectric constant, breakdown voltage, pulse voltage, etc. The refining depth, impurities, and moisture of the base oil all have a greater impact on the electrical performance of the oil. (15) Special physical and chemical properties of grease In addition to general physical and chemical properties, grease for special purposes also has its special physical and chemical properties. For example, grease with good water resistance requires water shower test; low-temperature grease needs to measure low-temperature torque; multi-effect grease needs to measure extreme pressure anti-wear and rust resistance; long-life grease needs bearing life test. There are corresponding test methods for the determination of these properties. (16) Other special physical and chemical properties In addition to the general properties, each oil should have its own unique special properties. For example, quenching oil should measure cooling rate; emulsified oil should measure emulsion stability; hydraulic rail oil should measure anti-climbing coefficient; spray lubricating oil should measure oil mist diffusion; refrigerating oil should measure flocculation point; low temperature gear oil should measure Ditch points and so on. These characteristics require the special chemical composition of the base oil, or the addition of some special additives to ensure it. 4. Simulated bench test After evaluating their special physical and chemical properties, lubricating oils generally have to undergo some simulation bench tests, including some engine tests, before they can be put into use after passing. Oils with extreme pressure and anti-wear properties must be evaluated for their extreme pressure and anti-wear properties. Commonly used testing machines include Timken ring block testing machine, FZG gear testing machine, Falex testing machine, roller fatigue testing machine, etc., all of which are used to evaluate the extreme pressure load resistance or wear resistance of oil products. The most common testing machine used to evaluate the extreme pressure performance of oil products is the four-ball machine, which can evaluate the maximum non-seizure load, sintering load, long-term wear and comprehensive wear index of the oil. These indexes can reflect the extreme pressure and anti-wear performance of oil products to a certain extent, but they have no good correlation with actual performance in many cases. This method is still widely used because it is simple and easy to implement. In the high-end vehicle gear oil standards, a series of gear bench evaluations are required, including low-speed, high-torque, high-speed and low-torque gear tests; gear tests with shock loads; gearbox corrosion tests and oil thermal oxidation stability gears test. There are many single-cylinder bench test methods for evaluating internal combustion engine oil, such as Pete W-1, AV-1, AV-B, Lebek L-38 single cylinder and domestic 1105, 1135 single cylinder, which can be used to evaluate various grades of internal combustion engine oil. In the current API quality classification standard for internal combustion engine oil, it is stipulated that diesel engine oil shall be assessed with Caterpillar, Mack, Cummins, single cylinder and GM multi-cylinder; for gasoline engine oil, MS program ⅡD (corrosion and wear resistance) ⅢE (high temperature oxidation) ⅤE (low temperature) Sludge) and other tests. These bench tests require a lot of investment and high cost for each test. They have strict requirements on test conditions, such as environmental control and fuel standards. Not all test laboratories can meet the evaluation conditions. Only a few can be set up nationwide. Assessment points, to assess these oil products. In short, due to the different characteristics of various oil products and the vastly different parts of use, it is necessary to formulate specifications reflecting the inherent quality level of each type of oil product according to the actual situation of each type of oil product, so that each type of oil product produced is Meet the required quality index, so as to meet the actual use requirements of the equipment. 5. Lubricating oil management Lubricating oil is the most widely used category among petrochemical products. At the same time, lubricating oil is a technology-intensive product. Only by doing a good job of lubricating oil management and using lubricating oil correctly can the technical performance of lubricating oil be brought into play, which can ensure the normal operation of equipment, prolong equipment life, save lubricating oil material, save energy, and improve economic and social benefits. Transportation and storage management of lubrication The transportation and storage requirements of lubricating oil mainly include:(1) Bulk oil products

1. Containers for holding and storing lubricating oil must be clean and clean; 2. Transportation and storage of transformer oil and steam turbine oil require "special tank line"; other oil products shall be in accordance with internal combustion engine oil, hydraulic oil, and gear oil. Set up storage and transportation facilities for major products. 3. Special attention should be paid to prevent the mixing of water and impurities during transportation and storage. 4. The storage period of bulk lubricants should generally not exceed half a year. 5. The density of lubricating oil is about 0.75~0.95g/cm, which is lighter than water and insoluble in water. The flash point (opening) of lubricating oil is generally higher than 150℃, which is a combustible material. Care should be taken to prevent outflow during storage and transportation. Pollute the environment and catch fire. 6. Indicate the product name, brand number, grade, quantity and storage date, etc. 7. In principle, the same oil produced by different manufacturers cannot be mixed storage. If mixed storage is not possible, the "mixed pair test" should be performed first to confirm that there is no adverse reaction before operation. (2) Barreled oil products 1. Crude operations are strictly prohibited on oil product loading and unloading trucks, and the height of oil products should be properly stacked to avoid danger or crushing products. 2. Special attention should be paid to prevent mixing of water and impurities during transportation and storage. 3. The storage period of barreled lubricants can be longer than that of bulk, but generally should not exceed one year.

4. Different oil products should be stacked separately and clearly marked with the product name, brand, grade, quantity and storage, etc., so as to avoid mistakes in the management of the lubricant use process during delivery (1) Selection of lubricants The first link is the key to ensure reasonable lubrication of equipment and give full play to lubricant performance.

1. The selection of lubricating oil should comprehensively consider the following three factors: (1) the working conditions (ie working conditions) of the mechanical equipment in actual use; (2) the designation or recommendation of the mechanical equipment manufacturer's manual; (3) the manufacturing of lubricating oil Manufacturer’s regulations or recommendations. 2. Selection of Lubricant Performance Index (1) Viscosity Viscosity is an index for the classification and classification of various lubricants, which is of decisive significance for quality identification and determination. The viscosity of the lubricating oil used in the equipment is determined according to the design or calculation data by checking the relevant chart. (2) Pour point Pour point is an indirect indicator of low-temperature fluidity of lubricating oil during storage, transportation and use. Experience has proved that the operating temperature of general lubricating oil must be 5~10℃ higher than the pour point. (3) Flash point Flash point is mainly an indicator of the safety of lubricating oil storage, transportation and use, and it is also an indicator of controlling lubricating oil fraction and volatility during production. The principle of the specification of the flash point index of lubricating oil is to leave a safety factor of 1/2 in accordance with the safety regulations, that is, it is 1/2 higher than the actual use temperature. For example, the oil temperature of the internal combustion engine oil pan does not exceed 120°C, so the minimum flash point of the internal combustion engine oil is 180°C. (4) There are many performance indicators selected for performance indicators, and there is a large gap between different varieties. It should be reasonably determined based on the operating conditions of the equipment, the requirements of the manufacturer, and the description and introduction of oil products. Strive to meet the requirements of lubrication technology and be economical and reasonable. (2) Substitution of lubricating oil 1. Different types of lubricating oil have their particularities or differences in their performance. Therefore, it is required to select lubricating oil correctly and reasonably, avoid substitution, and do not allow random substitution.

2. The principle of lubricant substitution (1) Try to use the same type of oil or oil with similar performance as a substitute. (2) The viscosity should be equivalent, and the viscosity of the substitute oil should not exceed ±15% of the original oil. Priority should be given to oils with higher viscosity for substitution. (3) The quality is high and low. (4) The environment and working temperature of the equipment should also be considered when selecting substitute oil. (3) Mixed use of lubricating oil 1. Different types of brands, different manufacturers, and new and old oils should be avoided as much as possible. The following oil products are absolutely prohibited from mixing. (1) Military special oil and special oil cannot be mixed with other oils. (2) Oil products with anti-emulsification performance requirements shall not be mixed with oil products without anti-emulsification requirements. (3) Anti-ammonia turbine oil shall not be mixed with other turbine oils. (4) Zn-containing anti-wear hydraulic oil cannot be mixed with anti-silver hydraulic oil. (5) Gear oil cannot be mixed with worm gear oil. 2. The following situations can be used together: (1) Products of the same type with similar quality from the same manufacturer. (2) Products of the same manufacturer with different brands. (3) Different types of oil products, if it is known that the two components of the blending do not contain additives. (4) There is no abnormal phenomenon and obvious performance change of different types of oil products after mixed use test. 3. There are many kinds of additives added to internal combustion engine oil, and the performance is different; the mixed use of oils that do not understand the performance must be cautious. In order to avoid adverse consequences or even equipment lubrication accidents. (4) Control of lubricating oil pollution Lubrication accidents are mainly caused by pollution except for the selection or improper use of lubricating oil. 1. The substances that pollute lubricating oil include dust, impurities, and water. 2. The pollution control is very important for the anti-wear performance of hydraulic oil, turbine oil, hydrostatic oil film bearing oil and high-speed bearing oil. 3. Measures to control pollution: (1) The container for storing and transporting lubricating oil must be clean, airtight, and not in contact with copper, tin and other metals that can easily promote the oxidation and deterioration of lubricating oil. (2) Settlement and filtration treatment should be carried out before oil products are added to the equipment to ensure that the cleanliness is above five. (3) The fueling container should not be exposed to the atmosphere, especially the fueling container should not be left uncovered. (4) Oil tanks storing lubricating oil should be cleaned regul